Intro to photosynthesis (AH lect 1)

Question 1

Complexes involved in oxygenic photosynthetic ETC

Answer 1

PS2
Cytochrome b6f
Plastocyanin
PS1

-linear ETC

Question 2

Complexes involved in anoxygenic photosynthetic ETC

Answer 2

RC
Cytochrome bc1
Cytochrome c2

-cyclic ETC

Question 3

Chloroplast/Cyanobacteria site of oxygenic photosynthesis

Answer 3

thylakoid membranes
-highly folded (large SA)

grana = stacked thylakoids
lamella = unstacked, connecting membranes

Question 4

Purple bacteria site of anoxygenic photosynthesis

Answer 4

Intracytoplasmic membranes
-Lamella
-Vesicular

Question 5

Chlorophyll excitation

Answer 5

-e- in conjugated pi-e- system absorbs light and is promoted from ground state to either S1 or S2 state
-if in S2 state, e- rapidly looses energy and drops to S1 (internal conversion)
-from S1 state, e- returns to ground state either by internal conversion or fluorescence (emitting a photon)

-visualised on Jablonski diagram

Question 6

FRET

Fluorescence resonance energy transfer

Answer 6

non-radiative transfer of energy from excited donor to acceptor
-only happens if donor and acceptor close in distance to eachother and have a spectral overlap

Question 7

What does the efficiency of FRET depend on?

Answer 7

-spectral overlap of donor’s fluorescence emission and acceptor’s absorbance
-distance between donor and acceptor (<5nm)

Question 8

Why do different (bacterio)chlorophylls absorb different wavelengths of light?

Answer 8

modifications to asymmetic chlorophyll affects distribution of e- in pi-e- system

interactions with scaffold proteins and nearby pigments also alter absorbance

-gives pigments different energetic and spectroscopic properties

Question 9

What are the role of accessory proteins?

Answer 9

fill the spectral gap (500-650nm) where chlorophylls don’t absorb
eg. carotenoids, bilins (in cyanobacteria and algae)

Question 10

What are the roles of carotenoids?

Answer 10

-fill the spectral gap (500-650nm) where chlorophylls don’t absorb and transfer energy to chlorophylls (N/B: carotenoid must be closer to chlorophyll compared to chlorophyll-chlorophyll transfer bc carotenoids have a shorter lifetime)
-photoprotection by non-chemical quenching of harmful triplet excited states of chlorophylls

Question 11

Special pair chlorophylls

Answer 11

-RC
-redox active